In a large mixing bowl, combine the lean ground beef, diced onion, minced garlic, grated parmesan cheese, Italian breadcrumbs, chopped parsley, salt, pepper, egg, and milk. Mix until well incorporated, being careful not to overmix.
Shape the mixture into meatballs about 1 to 1.5 inches in diameter and place them on a plate or baking sheet.
Preheat your air fryer to 400°F (200°C). This ensures even cooking and a crispy exterior.
Arrange the meatballs in the air fryer basket in a single layer, cooking for about 10-12 minutes until browned and cooked through.
Remove the meatballs from the air fryer and let them rest for a few minutes before serving with marinara sauce, over pasta, or in a sub sandwich.
